IBS: a connection between the brain, the microbiota, and the gut

For the first time, researchers have established a connection between the composition of the intestinal flora and changes in certain brain regions in people suffering from irritable bowel syndrome (IBS).

Many studies have suggested that the gut-brain axis plays a role in IBS. The disorder seems to be associated with dysbiosis in the intestinal microbiota, structural anomalies in the brain, and an impact of psychiatric disorders on the composition of the intestinal flora. A California team explored all of these dimensions at once in patients with IBS.

The study included 29 patients with IBS and 23 healthy subjects as controls (HC). The authors analyzed the composition of their intestinal microbiota, evaluated their mental condition with questionnaires (particularly regarding the occurrence of traumatic childhood events), and studied certain regions of the brain by neuroimaging.

Two subgroups of patients with IBS were identified: one presented a microbiota specific to IBS (IBS1 subgroup) and the other had a microbiota identical to that of healthy subjects (HC-like IBS subgroup). The first is characterized by an elevated ratio Firmicutes/Bacteroides, greater microbial diversity, and an increased abundance of certain classes, particularly Bacilli and Clostridia and the genus Holdemania, when compared to the HC-like IBS group. The two types of microbiota were not linked to types of symptoms (constipation, diarrhea, or mixed), anxiety, or stress. However, IBS1 subjects had elevated scores for childhood trauma compared to the others. Furthermore, researchers noted correlations between an increase in the volume of certain sensory and motor areas of the brain (thalamus, basal ganglia, and precentral gyrus) and an overabundance of Clostridia or a deficit of Bacteroidia observed in the IBS1 group. Lastly, the shape of the posterior insula, involved in emotions, was correlated with an increased expression of twenty bacterial genes in the IBS1 group, including two involved in the metabolism of neurotransmitters and two more involved in the metabolism of short-chain fatty acids.

According to the authors, this is the first study to demonstrate a connection between the composition of the intestinal microbiota and changes in certain areas of the brain in patients presenting with IBS.